We used some Cascade oil in a batch of ESB to cover a metallic taint due to poor welds not being passivated. The amount was 15cc to 16 or 18 barrels. That batch took a long time to mellow. That worked out to 0.9375 to 0.833 cc per barrel divided by 31.0 was about 0.03 to 0.0268 cc. per gallon. So you would need a couple of drops, added one at a time cut with Everclear or good grade Vodka. If you don't have the oil or it is too costly you can make a 'hop tea' by steeping some of your finishing hops in a bag and add the cooled extract to your secondary or racking bucket.